Piezoelectric actuator, method of manufacturing same, and liquid ejection head

ABSTRACT

The piezoelectric actuator comprises: a supporting substrate; a thermal stress controlling layer which is formed on the supporting substrate; and a piezoelectric body which is formed as a film onto the thermal stress controlling layer on the supporting substrate at a higher temperature than room temperature, wherein the thermal stress controlling layer reduces a film stress induced by formation of the piezoelectric body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric actuator, a method ofmanufacturing same, and a liquid ejection head, and more particularly totechnologies that can reduce a thermal stress induced by film formationof a piezoelectric body.

2. Description of the Related Art

Conventionally, the principal method of manufacturing an inkjet head isa method which involves bonding a bulk polished piezoelectric bodymember (made of lead zirconate titanate (Pb(ZrTi)O₃) (PZT), for example)and a calcined green sheet, to a diaphragm plate, by means of anadhesive. In this case, there is no need to take account of thermalstress in the piezoelectric body.

Furthermore, in a method of manufacturing inkjet head described inJapanese Patent Application Publication No. 2003-309299, a piezoelectricfilm is grown epitaxially on an epitaxial substrate, a silicon substrateis bonded directly to the opposite side of the piezoelectric film, andthen the epitaxial substrate is separated from the piezoelectric film.In this case, the thermal stress induced on the boundary between thepiezoelectric film and the epitaxial substrate by the formation of thepiezoelectric film can be eliminated by removing the epitaxialsubstrate.

Moreover, recently, it is necessary to form the piezoelectric body as athin film in accordance with increasing density in inkjet heads.Therefore, there are various examples that a piezoelectric body isformed on a diaphragm plate by the sputtering method.

On the other hand, recently, in the field of micro electrical mechanicalsystems (MEMS), technologies are suggested that elements such as sensorsand actuators are integrated in yet higher levels by using piezoelectricceramic, and are forming films on those elements in order to achievepractical use. An aerosol deposition method receives attention in thosetechnologies, which is known as a film formation technique for use withceramics, metals, and the like.

The aerosol deposition method is a method in which an aerosol isgenerated from a powder of raw material, the aerosol is sprayed onto asubstrate, and a film is formed by deposition of the powdered materialdue to its impact energy. It is also called a “spray volume method” or a“gas deposition volume method”.

When manufacturing a liquid ejection head, such as an inkjet head, it isproposed that a piezoelectric body and the like may be formed by theaerosol deposition method described above (see Japanese PatentApplication Publication No. 2003-136714).

The film thickness of a piezoelectric body formed by the sputteringmethod on a diaphragm is approximately 3 μm. Therefore, since the filmis thin, it does not give rise to notable deformation of the diaphragmeven if there is stress in the film. Hence, no particular importance isattached to controlling stress in the film.

On the other hand, if a piezoelectric body or the like is formed by theaerosol deposition method, as described in Japanese Patent ApplicationPublication No. 2003-136714, a strong compressive stress acts in theaerosol deposition film which has a fine structure, and the temperatureduring aerosol deposition film formation is approximately 600° C.Therefore, thermal stress acts on the film after film formation due tothe difference between thermal expansion coefficients of thepiezoelectric body and the diaphragm, and in particular, when the filmis formed on a thin diaphragm having a thickness of 30 μm or less, thenthe diaphragm deforms due to the stress. Furthermore, if the filmthickness of the piezoelectric body is 1 μm or more, and moreparticularly, approximately 10 μm, then the deformation due to stress inthe film occurs remarkably.

FIG. 13A shows an ideal state in which there is no film stress in apiezoelectric body 2 formed on a diaphragm 1, so that there is nodeformation of the diaphragm 1. FIG. 13B shows a state where acompressive stress acts on the piezoelectric body 2, so that thediaphragm 1 deforms unevenly due to the stress.

When stress deformation occurs in the diaphragm 1 as shown in FIG. 13B,there are following problems.

(1) Since a gap arises when the diaphragm 1 is bonded to the ink chamberpartitions 3, the following problems arise, consequently.

-   -   a) Since the ink chambers 4 cannot be divided by the ink chamber        partitions 3, then there is movement of ink between adjacently        positioned ink chambers 4, and ink may gather in the gaps,        thereby making it impossible to control the volume of ink that        is ejected from the nozzles.    -   b) Since regions where the diaphragm 1 is not fixed to the ink        chamber partitions 3 arise, then variations occur in the        displacement volume and torque, and hence image defects arise        due to non-uniformities in ink ejection throughout the surface.    -   c) Since the diaphragm 1 and the ink chamber partitions 3 can        not be reliably fixed by bonding, then long-term durability        cannot be guaranteed.

(2) Since deformation occurs in the diaphragm 1, then the volume of theink chamber 4 varies, and variation may arise in the ejected ink volumeeven if the diaphragm 1 is driven at the same displacement volume,whereby image defects may occur due to non-uniformities in ink ejectionthroughout the surface.

(3) When deformation occurs in the diaphragm 1, sufficient alignmentaccuracy is not obtained in the subsequent process of wiring to theelectrodes for driving the piezoelectric bodies 2, whereby wiringdefects arise.

SUMMARY OF THE INVENTION

The present invention was devised in view of the aforementionedcircumstances, an object thereof being to provide a piezoelectricactuator, a method of manufacturing same, and a liquid ejection headthat can reduce either the film stress in piezoelectric bodies formedonto a supporting substrate and the deformation of the supportingsubstrate, without restricting the material of the support substrate.

In order to attain the aforementioned object, the present invention isdirected to a piezoelectric actuator comprising: a supporting substrate;a thermal stress controlling layer which is formed on the supportingsubstrate; and a piezoelectric body which is formed as a film onto thethermal stress controlling layer on the supporting substrate at a highertemperature than room temperature, wherein the thermal stresscontrolling layer reduces a film stress induced by formation of thepiezoelectric body.

In the case in which no thermal stress controlling layer is interposedbetween the supporting substrate and the piezoelectric body, a thermalstress acts on the piezoelectric body when the piezoelectric bodyreturns to normal temperature after film formation of the piezoelectricbody, due to the difference between thermal expansion coefficients ofthe supporting substrate and the piezoelectric body, and the temperaturedifference between normal temperature and a temperature during filmformation. In this case, a stress (compressive stress) also acts on theactual piezoelectric body. However, according to the present invention,since the thermal stress controlling layer is interposed, then the filmstress in the piezoelectric body is reduced, and deformation of thesupporting substrate is suppressed. Incidentally, it is considered thatthe stress of the piezoelectric body can be reduced by selecting asupporting substrate having a thermal expansion coefficient which isclose to the thermal expansion coefficient of the piezoelectric body,but in this case, a restriction is placed on the thermal expansioncoefficient of the supporting substrate, in addition to the durability,processability, and vibration characteristics (such as Young's modulus)of the supporting substrate. The present invention can increase choiceflexibility of materials which can be used as the supporting substrate,without restricting the thermal expansion coefficient of the supportingsubstrate.

The present invention is also directed to the piezoelectric actuatorwherein: the thermal stress controlling layer has a thermal expansioncoefficient which is selected according to a first thermal expansioncoefficient and a second thermal expansion coefficient, the firstthermal expansion coefficient being a thermal expansion coefficient ofpiezoelectric body, the second thermal expansion coefficient being athermal expansion coefficient of the supporting substrate. In otherwords, the layer having a thermal expansion coefficient which can reducethermal stress of the piezoelectric body is selected as the thermalstress controlling layer.

The present invention is also directed to the piezoelectric actuatorwherein: when the second thermal expansion coefficient is higher thanthe first thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is lower than the secondthermal expansion coefficient. Therefore, it is possible to decrease adifference between thermal expansion coefficients of the piezoelectricbody and the thermal stress controlling layer on the supportingsubstrate.

The present invention is also directed to the piezoelectric actuatorwherein: when the second thermal expansion coefficient is higher thanthe first thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is lower than the firstthermal expansion coefficient. According to the present invention, it ispossible to allow the thermal stress controlling layer to cancel out thetrue stress in the piezoelectric film and the thermal stress.

The present invention is also directed to the piezoelectric actuatorwherein: when the second thermal expansion coefficient is lower than thefirst thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is higher than thesecond thermal expansion coefficient. Accordingly, it is possible todecrease a difference between thermal expansion coefficients of thepiezoelectric body and the thermal stress controlling layer on thesupporting substrate.

The present invention is also directed to the piezoelectric actuatorwherein: when the second thermal expansion coefficient is lower than thefirst thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is higher than the firstthermal expansion coefficient. Accordingly, it is possible to allow thethermal stress controlling layer to cancel out the true stress in thepiezoelectric film and the thermal stress.

The present invention is also directed to the piezoelectric actuatorwherein the thermal stress controlling layer has a prescribed thicknessrequired for reducing a thermal stress remaining in the piezoelectricbody. As a thickness of the thermal stress controlling layer increases,the thermal expansion coefficient of the thermal stress controllinglayer is more dominant than the thermal expansion coefficient of thesupporting substrate.

The present invention is also directed to the piezoelectric actuatorwherein the thermal stress controlling layer also serves as an electrodefor driving the piezoelectric body.

The present invention is also directed to the piezoelectric actuatorwherein an electrode which drives the piezoelectric body is formedbetween the thermal stress controlling layer and the piezoelectric body.This electrode can account for a part of the thermal stress controllinglayer, depending on the thickness thereof.

The present invention is also directed to the piezoelectric actuatorwherein a thickness of the supporting substrate is 30 μm or less.

The present invention is also directed to the piezoelectric actuatorwherein a thickness of the piezoelectric body is 1 μm or greater.

More specifically, in a piezoelectric actuator for achieving apiezoelectric inkjet head having a high precision and a high-torque, itis important that a thick film of piezoelectric body of 1 μm or greater(preferably, approximately 10 μm) be formed directly onto a thinsupporting substrate (diaphragm) having a thickness of 30 μm or less(preferably, approximately 15 μm).

The present invention is also directed to the piezoelectric actuatorwherein the piezoelectric body is formed by an aerosol depositionmethod. Since the piezoelectric body is formed by the aerosol depositionmethod, it is possible to form the piezoelectric body having a thicknesswhich can not be formed by the spattering method, for example.

The present invention is also directed to the piezoelectric actuatorwherein: the piezoelectric body formed by the aerosol deposition methodis a PZT piezoelectric film; and a crystal a-axis length of the PZTpiezoelectric film is in the range of 2.025 to 2.040 Angstroms. When thecrystal a-axis length of the PZT piezoelectric film is in the range of2.025 to 2.040 Angstroms, it is possible to prevent the supportingsubstrate from being deformed largely by the film stress in the PZTpiezoelectric film.

The present invention is also directed to the piezoelectric actuatorwherein the thermal stress controlling layer is formed by at least oneof a sputtering method, a plating method, and an aerosol depositionmethod. When the thermal stress controlling layer is formed by theaerosol deposition method, it is necessary to reduce the film stress inthe thermal stress controlling layer. In order to reduce the filmstress, for example, the thermal stress controlling layer is formed notto have a fine structure, such as a piezoelectric film, or the filmthickness and the materials for the thermal stress controlling layer arechosen.

The present invention is also directed to the piezoelectric actuatorwherein: the supporting substrate is made of stabilized zirconia; andthe thermal stress controlling layer is made of platinum having athickness of 2 to 5 μm. Generally, platinum has a thickness of 100 nmfor forming the electrode, but the platinum thickness of 2 to 5 μm isneeded for having function of the thermal stress controlling layer. Thethermal stress controlling layer having a thickness in this range can beformed by the aerosol deposition method.

The present invention is also directed to the piezoelectric actuatorwherein: the supporting substrate is made of stabilized zirconia; andthe thermal stress controlling layer is made of iridium having athickness of 1 to 5 μm. Since a thermal expansion coefficient of iridiumis smaller than that of platinum, then the thermal stress controllinglayer of iridium can have a thinner thickness than the thermal stresscontrolling layer of platinum.

The present invention is also directed to the piezoelectric actuatorwherein: the supporting substrate is made of silicon; and the thermalstress controlling layer is made of platinum having a thickness of 10 μmor less.

The present invention is also directed to the piezoelectric actuatorwherein: the supporting substrate is made of silicon; and the thermalstress controlling layer is made of nickel having a thickness of 1 to 5μm.

The present invention is also directed to the piezoelectric actuatorwherein: the supporting substrate is made of silicon; and the thermalstress controlling layer is made of titanium oxide having a thickness of2 to 5 μm. Since a thermal expansion coefficient of titanium oxide issmaller than that of nickel, then the thermal stress controlling layerof titanium oxide is thicker than the thermal stress controlling layerof nickel.

In order to attain the aforementioned object, the present invention isdirected to a liquid ejection head comprising: a pressure chamber whichfills with a liquid; a nozzle which ejects the liquid from the pressurechamber; and a piezoelectric actuator which comprises a supportingsubstrate; a thermal stress controlling layer which is formed on thesupporting substrate; and a piezoelectric body which is formed as a filmonto the thermal stress controlling layer on the supporting substrate ata higher temperature than room temperature, wherein the thermal stresscontrolling layer reduces a film stress induced by formation of thepiezoelectric body; and the supporting substrate is a diaphragm in whichthe liquid is ejected from the nozzle by changing a volume of thepressure chamber.

The present invention is also directed to the liquid ejection headwherein: the thermal stress controlling layer has a thermal expansioncoefficient which is selected according to a first thermal expansioncoefficient and a second thermal expansion coefficient, the firstthermal expansion coefficient being a thermal expansion coefficient ofpiezoelectric body, the second thermal expansion coefficient being athermal expansion coefficient of the supporting substrate.

The present invention is also directed to the liquid ejection headwherein: when the second thermal expansion coefficient is higher thanthe first thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is lower than the secondthermal expansion coefficient.

The present invention is also directed to the liquid ejection headwherein: when the second thermal expansion coefficient is higher thanthe first thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is lower than the firstthermal expansion coefficient.

The present invention is also directed to the liquid ejection headwherein: when the second thermal expansion coefficient is lower than thefirst thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is higher than thesecond thermal expansion coefficient.

The present invention is also directed to the liquid ejection headwherein: when the second thermal expansion coefficient is lower than thefirst thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is higher than the firstthermal expansion coefficient.

The present invention is also directed to the liquid ejection headwherein the thermal stress controlling layer has a prescribed thicknessrequired for reducing a thermal stress remaining in the piezoelectricbody.

The present invention is also directed to the liquid ejection headwherein the thermal stress controlling layer also serves as an electrodefor driving the piezoelectric body.

The present invention is also directed to the liquid ejection headwherein an electrode for driving the piezoelectric body is formedbetween the thermal stress controlling layer and the piezoelectric body.

The present invention is also directed to the liquid ejection headwherein a thickness of the supporting substrate is 30 μm or less.

The present invention is also directed to the liquid ejection headwherein a thickness of the piezoelectric body is 1 μm or greater.

The present invention is also directed to the liquid ejection headwherein the piezoelectric body is formed by an aerosol depositionmethod.

The present invention is also directed to the liquid ejection headwherein: the piezoelectric body formed by the aerosol deposition methodis a PZT piezoelectric film; and a crystal a-axis length of the PZTpiezoelectric film is in the range of 2.025 to 2.040 Angstroms.

The present invention is also directed to the liquid ejection headwherein the thermal stress controlling layer is formed by at least oneof a sputtering method, a plating method, and an aerosol depositionmethod.

The present invention is also directed to the liquid ejection headwherein: the supporting substrate is made of stabilized zirconia; andthe thermal stress controlling layer is made of platinum having athickness of 2 to 5 μm.

The present invention is also directed to the liquid ejection headwherein: the supporting substrate is made of stabilized zirconia; andthe thermal stress controlling layer is made of iridium having athickness of 1 to 5 μm.

The present invention is also directed to the liquid ejection headwherein: the supporting substrate is made of silicon; and the thermalstress controlling layer is made of platinum having a thickness of 10 μmor less.

The present invention is also directed to the liquid ejection headwherein: the supporting substrate is made of silicon; and the thermalstress controlling layer is made of nickel having a thickness of 1 to 5μm.

The present invention is also directed to the liquid ejection headwherein: the supporting substrate is made of silicon; and the thermalstress controlling layer is made of titanium oxide having a thickness of2 to 5 μm.

According to the present invention, the liquid ejection head can achievea high precision and a high-torque.

The present invention is directed to a method of manufacturing apiezoelectric actuator comprising the steps of: forming a thermal stresscontrolling layer on a supporting substrate; and forming a piezoelectricfilm by an aerosol deposition method in which an aerosol containing apowder of a piezoelectric material is sprayed onto the thermal stresscontrolling layer to accumulate the powder onto the thermal stresscontrolling layer, wherein the thermal stress controlling layer isformed in the step of forming the thermal stress controlling layer so asto have a thermal expansion coefficient and a thickness for reducingdeformation of the supporting substrate due to thermal stress in thepiezoelectric film.

According to the present invention, since a stress control layer isformed between the supporting substrate and the piezoelectric bodyformed directly on the supporting substrate, it is possible to reducethe film stress in the piezoelectric body formed on the supportingsubstrate, and hence, deformation of the supporting substrate can besuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of this invention, as well as other objects and advantagesthereof, will be explained in the following with reference to theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures and wherein:

FIG. 1 is a general schematic drawing of an inkjet recording apparatusaccording to an embodiment of the present invention;

FIG. 2 is a plan view of the principal components in the peripheral areaof a printing unit in the inkjet recording apparatus shown in FIG. 1;

FIG. 3 is a schematic drawing showing a film formation device accordingto an aerosol deposition method;

FIG. 4A is a graph showing a relationship between the thickness of apiezoelectric body made of PZT, the displacement volume, and thegenerated pressure, and FIG. 4B is a graph showing a relationshipbetween the thickness of a diaphragm, the displacement volume, and thegenerated pressure;

FIG. 5 is a principal cross-sectional diagram of the piezoelectricactuator according to a first embodiment of the present invention;

FIG. 6 is a graph showing a relationship between the film stress in thecase in which a PZT piezoelectric film is formed on a zirconiasubstrate, and the thickness of the stress buffer layer made ofplatinum;

FIG. 7 is a graph showing a relationship between the thermal expansioncoefficient of the diaphragm (supporting substrate) and the film stressin the PZT piezoelectric film;

FIG. 8 is a principal cross-sectional diagram of the piezoelectricactuator according to a second embodiment of the present invention;

FIG. 9 is a graph showing a relationship between the film thickness ofthe stress buffer layer made of platinum and the amount of stressdeformation in the silicon substrate, in the case in which a stressbuffer layer is interposed between the silicon substrate and the PZTpiezoelectric film;

FIG. 10 is a principal cross-sectional diagram of the piezoelectricactuator according to a third embodiment of the present invention;

FIG. 11 is a principal cross-sectional diagram of a liquid ejection headhaving a piezoelectric actuator;

FIG. 12 is a principal cross-sectional diagram of a liquid ejectionhead; and

FIG. 13A is a diagram showing an ideal state in which there is no filmstress in a piezoelectric body formed on a diaphragm so that there is nodeformation of the diaphragm, and FIG. 13B is a diagram showing a statein which a compressive stress acts on the piezoelectric body and thediaphragm deforms unevenly due to the stress.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

General Composition of Ink-Jet Recording Apparatus

Firstly, a general composition of an inkjet recording apparatus having aliquid ejection head according to the present invention will bedescribed below.

FIG. 1 is a general schematic diagram showing general composition of theinkjet recording apparatus according to an embodiment of the presentinvention. As shown in FIG. 1, the inkjet recording apparatus 10comprises: a printing unit 12 having a plurality of liquid ejectionheads (hereinafter simply called “head”) 12K, 12C, 12M, and 12Y for inkcolors of black (K), cyan (C), magenta (M), and yellow (Y),respectively; an ink storing and loading unit 14 for storing inks of K,C, M and Y to be supplied to the heads 12K, 12C, 12M, and 12Y; a papersupply unit 18 for supplying a recording paper 16; a decurling unit 20for removing curl in the recording paper 16; a suction belt conveyanceunit 22 disposed facing the nozzle face (ink-droplet ejection face) ofthe printing unit 12, for conveying the recording paper 16 while keepingthe recording paper 16 flat; a print determination unit 24 for readingthe printed result produced by the printing unit 12; and a paper outputunit 26 for outputting image-printed recording paper 16 (printed matter)to the exterior.

The recording paper 16 delivered from the paper supply unit 18 retainscurl due to having been loaded in the magazine. In order to remove thecurl, heat is applied to the recording paper 16 in the decurling unit 20by a heating drum 30 in the direction opposite from the curl directionin the magazine.

In the case of the configuration in which roll paper is used, a cutter(first cutter) 28 is provided as shown in FIG. 1, and the continuouspaper is cut into a desired size by the cutter 28. The cutter 28 has astationary blade 28A, of which length is not less than the width of theconveyor pathway of the recording paper 16, and a round blade 28B, whichmoves along the stationary blade 28A. The stationary blade 28A isdisposed on the reverse side of the printed surface of the recordingpaper 16, and the round blade 28B is disposed on the printed surfaceside across the conveyor pathway. When cut papers are used, the cutter28 is not required.

The decurled and cut recording paper 16 is delivered to the suction beltconveyance unit 22. The suction belt conveyance unit 22 has aconfiguration in which an endless belt 33 is set around rollers 31 and32 so that the portion of the endless belt 33 facing at least the nozzleface of the printing unit 12 and the sensor face of the printdetermination unit 24 forms a horizontal plane (flat plane).

The belt 33 has a width that is greater than the width of the recordingpaper 16, and a plurality of suction apertures (not shown) are formed onthe belt surface. A suction chamber 34 is disposed in a position facingthe sensor surface of the print determination unit 24 and the nozzlesurface of the printing unit 12 on the interior side of the belt 33,which is set around the rollers 31 and 32, as shown in FIG. 1. Thesuction chamber 34 provides suction with a fan 35 to generate a negativepressure, and the recording paper 16 on the belt 33 is held by suction.

The belt 33 is driven in the clockwise direction in FIG. 1 by the motiveforce of a motor (not shown) being transmitted to at least one of therollers 31 and 32, which the belt 33 is set around, and the recordingpaper 16 held on the belt 33 is conveyed from left to right in FIG. 1.

Since ink adheres to the belt 33 when a marginless print job or the likeis performed, a belt-cleaning unit 36 is disposed in a predeterminedposition (a suitable position outside the printing area) on the exteriorside of the belt 33.

A heating fan 40 is disposed on the upstream side of the printing unit12 in the conveyance pathway formed by the suction belt conveyance unit22. The heating fan 40 blows heated air onto the recording paper 16 toheat the recording paper 16 immediately before printing so that the inkdeposited on the recording paper 16 dries more easily.

The printing unit 12 is a so-called “full line head” in which a linehead having a is length corresponding to the maximum paper width isarranged in a direction (main scanning direction) that is perpendicularto the paper feed direction (see FIG. 2). Each of the heads 12K, 12C,12M, and 12Y is constituted by a line head, in which a plurality of inkejection ports (nozzles) are arranged along a length that exceeds atleast one side of the maximum-size recording paper 16 intended for usein the inkjet recording apparatus 10, as shown in FIG. 2.

The heads 12K, 12C, 12M, and 12Y are arranged in the order of black (K),cyan (C), magenta (M), and yellow (Y) from the upstream side, along thefeed direction of the recording paper 16. A color image can be formed onthe recording paper 16 by ejecting the inks from the heads 12K, 12C,12M, and 12Y, respectively, onto the recording paper 16 while conveyingthe recording paper 16.

The print determination unit 24 has a line sensor for capturing an imageof the ink-droplet deposition result of the printing unit 12, andfunctions as a device to check for ejection defects such as clogs of thenozzles in the printing unit 12 from the ink-droplet deposition resultsevaluated by the line sensor.

A post-drying unit 42 is disposed following the print determination unit24. The post-drying unit 42 is a device to dry the printed imagesurface, and includes a heating fan, for example. It is preferable toavoid contact with the printed surface until the printed ink dries, anda device that blows heated air onto the printed surface is preferable.

A heating/pressurizing unit 44 is disposed following the post-dryingunit 42. The heating/pressurizing unit 44 is a device to control theglossiness of the image surface, and the image surface is pressed with apressure roller 45 having a predetermined uneven surface shape while theimage surface is heated, and the uneven shape is transferred to theimage surface.

The printed matter generated in this manner is cut to a prescribed sizeby the cutter 28 and then output from the paper output unit 26. Thetarget print (i.e., the result of printing the target image) and thetest print are preferably output separately. In the inkjet recordingapparatus 10, a sorting device (not shown) is provided for switching theoutputting pathways in order to sort the printed matter with the targetprint and the printed matter with the test print, and to send them topaper output units 26A and 26B, respectively. When the target print andthe test print are simultaneously formed in parallel on the same largesheet of paper, the test print portion is cut and separated by a cutter(second cutter) 48.

Method for Forming Film According to Aerosol Deposition Method

Next, a method for forming film according to an aerosol depositionmethod as used in the manufacture of a piezoelectric actuator accordingto the present invention will be described below.

FIG. 3 is a schematic drawing showing a film formation device accordingto the aerosol deposition method. This film formation device has anaerosol generating chamber 52 in which a raw material powder 51 isprovided. Herein, the term “aerosol” includes fine particles of a solidor liquid which are suspended in a gas.

A carrier gas input section 53, an aerosol output section 54, and avibrating unit 55 are attached to the aerosol generating chamber 52.When a gas such as nitrogen gas (N₂) is introduced via the carrier gasinput section 53, the raw material powder is blown and lifted in theaerosol generating chamber 52, thereby generating an aerosol. In thiscase, if a vibration is applied to the aerosol generating chamber 52 bymeans of the vibrating unit 55, then the raw material powder is churnedup, thereby generating an aerosol efficiently. Thus, the generatedaerosol is channeled through the aerosol output section 54 to a filmformation chamber 56.

An exhaust tube 57, a nozzle 58, and a movable stage 59 are provided inthe film formation chamber 56. The exhaust tube 57 is connected to avacuum pump, and evacuates the interior of the film formation chamber56. After the aerosol is generated in the aerosol generating chamber 52and is conducted to the film formation chamber 56 via the aerosol outputsection 54, the aerosol is sprayed from the nozzle 58 onto a supportingsubstrate 50. Hence, the raw material powder collides with thesupporting substrate 50, and builds up thereon. The supporting substrate50 is mounted on the movable stage 59 that is capable ofthree-dimensional movement, and hence the relative positions of thesupporting substrate 50 and the nozzle 58 can be adjusted by controllingthe movable stage 59.

Target Thickness of Piezoelectric Body and Supporting Substrate

In order to achieve a liquid ejection head of high density, thedimensions of the piezoelectric body are set to 300 μm square, and thedimensions of the supporting substrate (diaphragm) are set to 500 μmsquare.

FIG. 4A is a graph showing a relationship between the thickness of apiezoelectric body made of lead zirconate titanate (Pb(ZrTi)O₃) (PZT)under the aforementioned conditions, the displacement volume, and thegenerated pressure. FIG. 4B is a graph showing a relationship betweenthe thickness of a diaphragm, the displacement volume, and generatedpressure.

As shown in FIG. 4A, if the liquid droplet size (target volume) of theliquid ejection head is set to x picoliters (pl) and the target pressureis set to y Megapascal (MPa), then the thickness of a PZT film is 10 μmto satisfy both the target volume and the target pressure.

Similarly, as shown in FIG. 4B, when the target volume is set to x (pl),and the target pressure is set to y (MPa), then the thickness of adiaphragm is 15 μm to satisfy both the target volume and the targetpressure.

When forming PZT directly onto a diaphragm, a film can only be formed toa thickness of approximately 3 μm by the sputtering method. Therefore,it is preferably to use the aerosol deposition method in order to formthe PZT film of 10 μm as described above.

Structure of Piezoelectric Actuator

As described above, when a PZT piezoelectric body having a thickness of10 μm is formed by the aerosol deposition method on a diaphragm having athickness of 15 μm, then a strong compressive stress acts on the actualPZT piezoelectric film having a fine structure, while thermal stressalso acts due to the difference between the thermal expansioncoefficients of the PZT piezoelectric film and the diaphragm, and hencethe diaphragm undergoes stress deformation due to the stress in the PZTpiezoelectric film. Therefore, the present invention attempts to reducethe film stress in the PZT piezoelectric film (in other words, tosuppress stress deformation in the diaphragm), by interposing a thermalstress controlling layer between the diaphragm and the PZT piezoelectricfilm along with altering the thermal expansion coefficient and thicknessof this thermal stress controlling layer.

First Embodiment: Case in which Thermal Expansion Coefficient ofDiaphragm is Higher than that of Piezoelectric Body

In the case in which the thermal expansion coefficient of the diaphragmis higher than that of the piezoelectric body, then a thin film made ofa material having a lower thermal expansion coefficient than thediaphragm (preferably, a thermal stress controlling layer (stress bufferlayer) made of a material having a lower thermal expansion coefficientthan the piezoelectric body) is formed previously on the diaphragm.

FIG. 5 is a principal cross-sectional diagram of a piezoelectricactuator 60 according to a first embodiment. As shown in FIG. 5, thepiezoelectric actuator 60 comprises: a stabilized zirconia substrate 62(thermal expansion coefficient: 9.9×10⁻⁶/° C.) as the diaphragm; and aPZT piezoelectric film 64 (thermal expansion coefficient: 9.5×10⁻⁶/° C.)as the piezoelectric body. The stabilized zirconia substrate(hereinafter referred to as simply “zirconia substrate”) 62 can be madeof calcia (CaO) stabilized zirconia (ZrO₂) or magnesia (MgO) stabilizedzirconia, more preferably yttria (Y₂O₃) stabilized zirconia. A stressbuffer layer 66 made of platinum (Pt) (thermal expansion coefficient:8.8×10⁻⁶/° C.) which has a lower thermal expansion coefficient than PZTis formed between the zirconia substrate 62 and the PZT piezoelectricfilm 64.

The stress buffer layer 66 is formed on the zirconia substrate 62 by thesputtering method, the plating method, or the aerosol deposition method.The PZT piezoelectric film 64 is formed on the stress buffer layer 66 bythe aerosol deposition method. The temperature during film formation bythe aerosol deposition method is approximately 600° C.

FIG. 6 is a graph showing the relationship between the film stress inthe case in which a PZT piezoelectric film 64 is formed on a zirconiasubstrate 62, and the thickness of the stress buffer layer 66. On thegraph in FIG. 6, the target film stress (40 MPa) is the target value forthe film stress at which the deformation of the substrate can be kept to10 μm (corresponding to the thickness of the adhesive) or less.

As shown on the graph in FIG. 6, when the film thickness of the stressbuffer layer 66 is zero (in other words, when no stress buffer layer 66is formed), then the film stress (compressive stress) in the PZTpiezoelectric film 64 becomes a maximum. As the film thickness of thestress buffer layer 66 becomes greater, then the state approaches thatof a film formed on a platinum substrate, and therefore, it is foundthat the actual film stress approaches a film stress corresponding to anideal platinum substrate.

According to the graph shown in FIG. 6, it is found that the stressreaches the target film stress (−40 MPa) when the film thickness of thestress buffer layer 66 is 2 μm.

On the other hand, FIG. 7 is a graph showing a relationship between thethermal expansion coefficient of the diaphragm (supporting substrate)and the film stress in the PZT piezoelectric film.

According to the graph in FIG. 7, when the thermal expansion coefficientof the supporting substrate is approximately 8×10⁻⁶/° C., then the filmstress in the PZT piezoelectric film is zero. In this case, the thermalexpansion coefficient of the supporting substrate (approximately,8×10⁻⁶/° C.) is smaller than the thermal expansion coefficient of thePZT piezoelectric film (approximately, 9.5×10⁻⁶/° C.), and hence it doesnot match the thermal expansion coefficient of the PZT piezoelectricfilm. This is because a large compressive stress acts on the PZTpiezoelectric film which has a fine structure formed by the aerosoldeposition method, and the thermal expansion coefficient of thesupporting substrate which enables the film stress in the PZTpiezoelectric film to be reduced to zero is a value (approximately8×10⁻⁶/° C.) which allows the aforementioned compressive stress to becancelled out by thermal stress. This value is smaller than the thermalexpansion coefficient of the PZT piezoelectric film.

On the graph in FIG. 7, when a supporting substrate has a thermalexpansion coefficient of 8.8×10⁻⁶/° C. corresponding to that ofplatinum, the predicted film stress is −60 MPa. This predicted filmstress virtually coincides with experimental results of a case in whicha platinum stress buffer layer 66 is formed on a zirconia substrate 62.

As described above, it has been confirmed that, when the thermalexpansion coefficient of the diaphragm is greater than that of thepiezoelectric body, a thin film (stress buffer layer) is formed betweenthe diaphragm and the piezoelectric body so as to have a thermalexpansion coefficient which is lower than the thermal expansioncoefficient of the piezoelectric body, and the thickness of this thinfilm is controlled, thereby being able to relieve the true stress in thepiezoelectric film by means of thermal stress.

As is evident from FIG. 6, if a thickness of platinum is 2 μm, then thetensile stress caused by thermal stress is not sufficient. Therefore,the compressive stress in the PZT piezoelectric film is not cancelledout completely. If the PZT piezoelectric film 64 is formed on thezirconia substrate 62, then it is possible to in cancel out film stresseffectively by introducing a stress buffer layer which has a thermalexpansion coefficient lower than the coefficient (8.8×10⁻⁶/° C.) ofthermal expansion of platinum. For example, a film of iridium (Ir)having a thickness of 1 to 5 μm (thermal expansion coefficient:6.5×10⁻⁶/° C.) is effective as a stress buffer layer.

Second Embodiment: Case in which Thermal Expansion Coefficient ofDiaphragm is Lower than that of Piezoelectric Body

In the case in which the thermal expansion coefficient of the diaphragmis lower than that of the piezoelectric body, a thin film made of amaterial having a higher thermal expansion coefficient than thediaphragm (preferably, a thermal stress controlling layer (stress bufferlayer) made of a material having a higher thermal expansion coefficientthan the piezoelectric body) is formed previously on the diaphragm.

FIG. 8 is a principal cross-sectional diagram of a piezoelectricactuator 70 according to a second embodiment. As shown in FIG. 8, thepiezoelectric actuator 70 comprises a silicon (Si) substrate 72 (thermalexpansion coefficient: 3.5×10⁻⁶/° C.) as the diaphragm, and a PZTpiezoelectric film 64 (thermal expansion coefficient: 9.5×10⁻⁶/° C.) asthe piezoelectric body. A stress buffer layer 74 made of platinum(thermal expansion coefficient: 8.8×10⁻⁶/° C.) is formed between thesilicon substrate 72 and the PZT piezoelectric film 64, which has ahigher thermal expansion coefficient than silicon. Since the method forforming the stress buffer layer 74 and the PZT piezoelectric film 64 onthe silicon substrate 72 is similar to that of the first embodimentshown in FIG. 5, the description thereof is omitted here.

FIG. 9 is a graph showing a relationship between the film thickness ofthe stress buffer layer 74 and the amount of stress deformation in thesilicon substrate 72, in the case in which a stress buffer layer 74 isinterposed between the silicon substrate 72 and the PZT piezoelectricfilm 64.

When a platinum stress buffer layer 74 is not formed, there is a strongtensile stress due to the thermal stress caused by a difference betweenthe thermal expansion coefficient of the silicon substrate 72 and thethermal expansion coefficient of the PZT piezoelectric film 64, and thenthe amount of deformation is large. However, as the thickness of thestress buffer layer 74 increases, so the thermal expansion coefficientof the stress buffer layer 74 becomes dominant.

As shown in the graph of FIG. 9, it is found that, when the thickness ofplatinum stress buffer layer 74 reaches approximately 9 μm, the filmstress of the PZT piezoelectric film 64 is cancelled out, and then thedeformation by the film stress becomes zero.

The thermal expansion coefficient of platinum (8.8×10⁻⁶/° C.) is higherthan the thermal expansion coefficient of silicon (3.5×10⁻⁶/° C.), butlower than the thermal expansion coefficient of PZT (9.5×10⁻⁶/° C.).Therefore, although a thermal stress in the compressive direction doesnot act on the PZT piezoelectric film 64 from the platinum stress bufferlayer 74, the thermal stress in the tensile direction can be relievedeffectively, in comparison with the case in which the PZT piezoelectricfilm 64 is formed directly onto the silicon substrate 72. As shown inFIG. 7, a strong compressive stress acts essentially on the PZTpiezoelectric film 64. Therefore, when the thermal stress in the tensiledirection is relieved by means of the platinum stress buffer layer 74,the compressive stress in the PZT piezoelectric film 64 can be cancelledout by means of this relieved thermal stress (tensile stress).

Furthermore, it is expected that, when a stress buffer layer constitutedby a material which has a higher thermal expansion coefficient thanplatinum, more preferably a material having a higher thermal expansioncoefficient than PZT (for example, nickel (Ni) having a thermalexpansion coefficient of 13×10⁻⁶/° C.), is introduced instead of theplatinum stress buffer layer 74, the stress in the PZT piezoelectricfilm 64 can be cancelled out by a stress buffer layer which is thinnerthan a platinum stress buffer layer 74. More specifically, in the casein which the thermal expansion coefficient of the diaphragm is lowerthan that of the piezoelectric body, a stress buffer layer made of amaterial which has a higher thermal expansion coefficient than thepiezoelectric body is formed between the diaphragm and the piezoelectricbody, and the thickness of this stress buffer layer is controlled,thereby being able to cancel out the true stress in the piezoelectricfilm and the thermal stress to each other.

Third Embodiment: Case of Diaphragm+Stress Buffer Layer+Electrode+PZTPiezoelectric Body (i.e., a Plurality of Stress Buffer Layers)

The platinum stress buffer layers 66 and 74 shown in FIG. 5 and FIG. 8also serve as an electrode (lower electrode) for driving the PZTpiezoelectric film 64, but the stress buffer layer and the electrode maybe separately functionally.

FIG. 10 is a principal cross-sectional diagram of a piezoelectricactuator 80 according to a third embodiment. As shown in FIG. 10, thepiezoelectric actuator 80 comprises a silicon substrate 72 (thermalexpansion coefficient: 3.5×10⁻⁶/° C.) as the diaphragm, and a PZTpiezoelectric film 64 (thermal expansion coefficient: 9.5×10⁻⁶/° C.) asthe piezoelectric body. A stress buffer layer 82 made of nickel (thermalexpansion coefficient: 13×10⁻⁶/° C.) and a platinum electrode 84(thermal expansion coefficient: 8.8×10⁻⁶/° C.) are formed between thesilicon substrate 72 and the PZT piezoelectric film 64. The stressbuffer layer 82 has a higher thermal expansion coefficient than PZT, andthe platinum electrode 84 functions as the electrode. For example, thestress buffer layer 82 and the platinum electrode 84 are formed by thesputtering method, and the PZT piezoelectric film 64 is formed by theaerosol deposition method.

In this case, it is found that, when the film thickness of the platinumelectrode 84 is in the region of 1 μm or less, the stress buffer layer82 is dominant in controlling stress. Furthermore, it is also confirmedthat there are no problems with the electrode functions in a platinumelectrode 84 of 1 μm or less.

Titanium oxide (TiO₂) (thermal expansion coefficient: 10 to 15×10⁻⁶/°C.) is another possible candidate for the stress buffer layer besidesthe nickel film described above, and any other material may be used forsatisfying the prescribed conditions according to the thermal expansioncoefficient.

Manufacturing of Piezoelectric Actuator having AforementionedComposition and Inspection of Stress Deformation

FIG. 11 is a principal cross-sectional diagram of a liquid ejection head90 having a piezoelectric actuator of the aforementioned composition.

As shown in FIG. 11, the liquid ejection head 90 comprises: a lowerelectrode 92 as a stress buffer layer, which is formed on a siliconsubstrate 91 by the sputtering method; a PZT piezoelectric film 93 (300μm square) which is patterned onto the lower electrode 92 by the aerosoldeposition method; an upper electrode 94 which is formed on top of thePZT piezoelectric film 93; and a silicon diaphragm 95 which is formed onthe opposite side to the PZT piezoelectric film 93 by etching. Thespaces formed by etching the silicon diaphragm 95 are applied as aplurality of pressure chambers 96 filled with a liquid such as an ink,and the silicon substrate 91 surrounding the pressure chambers 96 isapplied as the pressure chamber walls. In this case, the thickness ofthe silicon diaphragm 95 was set to 15 μm.

In this inspection, the PZT piezoelectric film 93 was poled by applyinga DC electric field of 3 kV/mm between the lower and upper electrodes 92and 94 of the PZT piezoelectric film 93. Then, the silicon diaphragm 95was driven and displaced by applying a DC pulse electric field ofapproximately 1 kV/mm between the lower and upper electrodes 92 and 94,and a laser beam was directed onto the lower surface of the silicondiaphragm 95, thereby evaluating the operation of the piezoelectricactuator.

It was confirmed that, when no stress buffer layer was introduced, thesilicon diaphragm 95 was deformed by stress in the region correspondingto the PZT piezoelectric film 93, so that there was variation in theamount of displacement. On the other hand, it was confirmed that, when astress buffer layer was introduced, the amount of displacement wasstabilized between ±10%.

Quantification of Film Stress

The crystal a-axis length was evaluated by X-ray diffraction (XRD) inorder to quantify the film stress in the PZT piezoelectric film (aerosoldeposition film).

First, when the PZT micro-particles forming the starting material of theaerosol deposition film were evaluated by XRD in order to ascertain thestress-free state, the a-axis length was 2.034 Angstroms (Å). Next, whena bulk calcined object obtained by calcining PZT micro-particles at1250° C. was evaluated, the a-axis length was 2.030 Å. Consequently, thea-axis length of the PZT in a stress-free state was set to be betweenapproximately 2.025 and 2.040 Å. In other words, the average between thea-axis length (2.034 Å) of the PZT micro-particles and the a-axis length(2.030 Å) of the bulk calcined object), namely, 2.032±0.007 Å, is takento be PZT in a stress-free state. Herein, the upper and lower limitvalues of the range 2.025 to 2.040 Å described above are the values atwhich the amount of deformation of the diaphragm becomes ±10 μm, due tothe film stress of the PZT piezoelectric film. Furthermore, 10 μm is thethickness of the adhesive used to bond the diaphragm to the ink chamberwalls and the like.

In the case of introducing no stress buffer layer, the a-axis length ofthe PZT piezoelectric film formed by the aerosol deposition methodbecame 2.055 Å. On the other hand, in the case of an embodiment in whichthe film stress was reduced to 10%, it was confirmed that the a-axislength changed to 2.033 Å.

Structure of Liquid Ejection Head

FIG. 12 is a principal cross-sectional diagram of a liquid ejection head90′. In FIG. 12, identical reference numerals denote parts that arecommon to FIG. 11, and description thereof is omitted here.

As shown in FIG. 12, the liquid ejection head 90′ is formed by bonding anozzle plate 97 onto the lower surface of the silicon substrate 91 shownin FIG. 11.

A liquid (ink) is supplied via a liquid flow channel (not shown) to thepressure chambers 96. Therefore, when a silicon diaphragm 95 isdisplacing by driving PZT piezoelectric films 93, the liquid ejectionhead 90′ ejects ink of a prescribed liquid droplet size from nozzles 98formed in the nozzle plate 97.

As described above, the piezoelectric actuator according to the presentinvention is explained with reference to the case in which it is used asan actuator of a liquid ejection head, but it may also be used as anactuator in other devices. Furthermore, the liquid ejection headaccording to the present invention is used as a line-type inkjet headwhich ejects ink onto recording paper, but the present invention is notlimited to those. It may also be applied to a shuttle-type head whichmoves back and forth reciprocally in a direction perpendicular to theconveyance direction of the print medium. Moreover, the liquid ejectionhead according to the present invention may be used as an image forminghead which sprays a treatment liquid or water onto a recording medium,or may be used as a liquid ejection head for forming an image recordingmedium by spraying a coating liquid onto a base material.

It should be understood, however, that there is no intention to limitthe invention to the specific forms disclosed, but on the contrary, theinvention is to cover all modifications, alternate constructions andequivalents falling within the spirit and scope of the invention asexpressed in the appended claims.

1. A piezoelectric actuator, comprising: a supporting substrate; athermal stress controlling layer which is formed on the supportingsubstrate; and a piezoelectric body which is formed as a film onto thethermal stress controlling layer on the supporting substrate at a highertemperature than room temperature, wherein the thermal stresscontrolling layer reduces a film stress induced by formation of thepiezoelectric body.
 2. The piezoelectric-actuator as defined in claim 1,wherein: the thermal stress controlling layer has a thermal expansioncoefficient which is selected according to a first thermal expansioncoefficient and a second thermal expansion coefficient, the firstthermal expansion coefficient being a thermal expansion coefficient ofpiezoelectric body, the second thermal expansion coefficient being athermal expansion coefficient of the supporting substrate.
 3. Thepiezoelectric actuator as defined in claim 2, wherein: when the secondthermal expansion coefficient is higher than the first thermal expansioncoefficient, the thermal stress controlling layer has a thermalexpansion coefficient which is lower than the second thermal expansioncoefficient.
 4. The piezoelectric actuator as defined in claim 2,wherein: when the second thermal expansion coefficient is higher thanthe first thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is lower than the firstthermal expansion coefficient.
 5. The piezoelectric actuator as definedin claim 2, wherein: when the second thermal expansion coefficient islower than the first thermal expansion coefficient, the thermal stresscontrolling layer has a thermal expansion coefficient which is higherthan the second thermal expansion coefficient.
 6. The piezoelectricactuator as defined in claim 2, wherein: when the second thermalexpansion coefficient is lower than the first thermal expansioncoefficient, the thermal stress controlling layer has a thermalexpansion coefficient which is higher than the first thermal expansioncoefficient.
 7. The piezoelectric actuator as defined in claim 1,wherein the thermal stress controlling layer has a prescribed thicknessrequired for reducing a thermal stress remaining in the piezoelectricbody.
 8. The piezoelectric actuator as defined in claim 1, wherein thethermal stress controlling layer also serves as an electrode for drivingthe piezoelectric body.
 9. The piezoelectric actuator as defined inclaim 1, wherein an electrode which drives the piezoelectric body isformed between the thermal stress controlling layer and thepiezoelectric body.
 10. The piezoelectric actuator as defined in claim1, wherein a thickness of the supporting substrate is 30 μm or less. 11.The piezoelectric actuator as defined in claim 1, wherein a thickness ofthe piezoelectric body is 1 μm or greater.
 12. The piezoelectricactuator as defined in claim 1, wherein the piezoelectric body is formedby an aerosol deposition method.
 13. The piezoelectric actuator asdefined in claim 12, wherein: the piezoelectric body formed by theaerosol deposition method is a PZT piezoelectric film; and a crystala-axis length of the PZT piezoelectric film is in the range of 2.025 to2.040 Angstroms.
 14. The piezoelectric actuator as defined in claim 1,wherein the thermal stress controlling layer is formed by at least oneof a sputtering method, a plating method, and an aerosol depositionmethod.
 15. The piezoelectric actuator as defined in claim 1, wherein:the supporting substrate is made of stabilized zirconia; and the thermalstress controlling layer is made of platinum having a thickness of 2 to5 μm.
 16. The piezoelectric actuator as defined in claim 1, wherein: thesupporting substrate is made of stabilized zirconia; and the thermalstress controlling layer is made of iridium having a thickness of 1 to 5μm.
 17. The piezoelectric actuator as defined in claim 1, wherein: thesupporting substrate is made of silicon; and the thermal stresscontrolling layer is made of platinum having a thickness of 10 μm orless.
 18. The piezoelectric actuator as defined in claim 1, wherein: thesupporting substrate is made of silicon; and the thermal stresscontrolling layer is made of nickel having a thickness of 1 to 5 μm. 19.The piezoelectric actuator as defined in claim 1, wherein: thesupporting substrate is made of silicon; and the thermal stresscontrolling layer is made of titanium oxide having a thickness of 2 to 5μm.
 20. A liquid ejection head, comprising: a pressure chamber whichfills with a liquid; a nozzle which ejects the liquid from the pressurechamber; and a piezoelectric actuator which comprises a supportingsubstrate; a thermal stress controlling layer which is formed on thesupporting substrate; and a piezoelectric body which is formed as a filmonto the thermal stress controlling layer on the supporting substrate ata higher temperature than room temperature, wherein the thermal stresscontrolling layer reduces a film stress induced by formation of thepiezoelectric body; and the supporting substrate is a diaphragm in whichthe liquid is ejected from the nozzle by changing a volume of thepressure chamber.
 21. The liquid ejection head as defined in claim 20,wherein: the thermal stress controlling layer has a thermal expansioncoefficient which is selected according to a first thermal expansioncoefficient and a second thermal expansion coefficient, the firstthermal expansion coefficient being a thermal expansion coefficient ofpiezoelectric body, the second thermal expansion coefficient being athermal expansion coefficient of the supporting substrate.
 22. Theliquid ejection head as defined in claim 21, wherein: when the secondthermal expansion coefficient is higher than the first thermal expansioncoefficient, the thermal stress controlling layer has a thermalexpansion coefficient which is lower than the second thermal expansioncoefficient.
 23. The liquid ejection head as defined in claim 21,wherein: when the second thermal expansion coefficient is higher thanthe first thermal expansion coefficient, the thermal stress controllinglayer has a thermal expansion coefficient which is lower than the firstthermal expansion coefficient.
 24. The liquid ejection head as definedin claim 21, wherein: when the second thermal expansion coefficient islower than the first thermal expansion coefficient, the thermal stresscontrolling layer has a thermal expansion coefficient which is higherthan the second thermal expansion coefficient.
 25. The liquid ejectionhead as defined in claim 21, wherein: when the second thermal expansioncoefficient is lower than the first thermal expansion coefficient, thethermal stress controlling layer has a thermal expansion coefficientwhich is higher than the first thermal expansion coefficient.
 26. Theliquid ejection head as defined in claim 20, wherein the thermal stresscontrolling layer has a prescribed thickness required for reducing athermal stress remaining in the piezoelectric body.
 27. The liquidejection head as defined in claim 20, wherein the thermal stresscontrolling layer also serves as an electrode for driving thepiezoelectric body.
 28. The liquid ejection head as defined in claim 20,wherein an electrode for driving the piezoelectric body is formedbetween the thermal stress controlling layer and the piezoelectric body.29. The liquid ejection head as defined in claim 20, wherein a thicknessof the supporting substrate is 30 μm or less.
 30. The liquid ejectionhead as defined in claim 20, wherein a thickness of the piezoelectricbody is 1 μm or greater.
 31. The liquid ejection head as defined inclaim 20, wherein the piezoelectric body is formed by an aerosoldeposition method.
 32. The liquid ejection head as defined in claim 31,wherein: the piezoelectric body formed by the aerosol deposition methodis a PZT piezoelectric film; and a crystal a-axis length of the PZTpiezoelectric film is in the range of 2.025 to 2.040 Angstroms.
 33. Theliquid ejection head as defined in claim 20, wherein the thermal stresscontrolling layer is formed by at least one of a sputtering method, aplating method, and an aerosol deposition method.
 34. The liquidejection head as defined in claim 20, wherein: the supporting substrateis made of stabilized zirconia; and the thermal stress controlling layeris made of platinum having a thickness of 2 to 5 μm.
 35. The liquidejection head as defined in claim 20, wherein: the supporting substrateis made of stabilized zirconia; and the thermal stress controlling layeris made of iridium having a thickness of 1 to 5 μm.
 36. The liquidejection head as defined in claim 20, wherein: the supporting substrateis made of silicon; and the thermal stress controlling layer is made ofplatinum having a thickness of 10 μm or less.
 37. The liquid ejectionhead as defined in claim 20, wherein: the supporting substrate is madeof silicon; and the thermal stress controlling layer is made of nickelhaving a thickness of 1 to 5 μm.
 38. The liquid ejection head as definedin claim 20, wherein: the supporting substrate is made of silicon; andthe thermal stress controlling layer is made of titanium oxide having athickness of 2 to 5 μm.
 39. A method of manufacturing a piezoelectricactuator, comprising the steps of: forming a thermal stress controllinglayer on a supporting substrate; and forming a piezoelectric film by anaerosol deposition method in which an aerosol containing a powder of apiezoelectric material is sprayed onto the thermal stress controllinglayer to accumulate the powder onto the thermal stress controllinglayer, wherein the thermal stress controlling layer is formed in thestep of forming the thermal stress controlling layer so as to have athermal expansion coefficient and a thickness for reducing deformationof the supporting substrate due to thermal stress in the piezoelectricfilm.